1. Field of the Invention
The present invention relates to a magnetic head device and a magnetic disk drive which is capable of reading information from or writing to a magnetic recording medium, as the magnetic head device is kept in contact with the magnetic recording medium.
2. Description of the Related Art
Efforts continue to increase the recording density of a magnetic disk drive using a hard disk. Due to the increase of recording density, the spacing between a magnetic head device (called "head" hereinafter) and a magnetic recording disk (called "disk" hereinafter) serving as a magnetic recording medium, is decreasing. Ultimately, it will be necessary to read/write information on the disk as the head is kept in contact with the disk.
The most important problem for carrying out the contact reading/writing is to reduce wear of the head and the disk. In order to reduce the wear, it is necessary to keep the contact force applied between the head and the disk at a low level and stable.
A brief structure of a prior art head having a taper-flat type slider will be described with reference to FIG. 13.
A taper-flat type slider 100 has a slider surface 102 which is opposed to a disk 101. The slider surface 102 includes a tapered surface 102a being slanted in a direction close to the disk along the rotating direction of the disk(shown by the arrow in FIG. 13), and a flat surface 102b being substantially parallel to the disk, when the disk stops rotating. Dynamic pressure (gage pressure) Ph generated by fluid-flow caused by rotation of the disk is applied to the slider surface 102. According to the flying slider method used in a prior art hard disk drive, the slider 100 flies above the disk 101 at a predetermined distance by means of the dynamic pressure Ph. In this case, however, the trailing edge serving as a contact portion 103 of the slider 102 is kept in contact with the surface of the disk 101. A magnetic pole(not shown) is mounted on the contact portion 103 to read/write information on the disk 101, as the magnetic pole is kept in contact with the disk.
There are three forces being applied to the slider 100 when the disk 101 rotates. They are a load F, a fluid force fh, and a contact force fc. The load F is applied at a pivot position 104 by a suspension (not shown). The fluid force is a sum of the dynamic pressure Ph. It is applied at the position 105 at the center of the distribution of the dynamic pressure Ph. The contact force is applied at the contact portion 103 from the disk 101.
The relation of these forces (F, fh, fc) is shown in the following equation (1). ##EQU1##
"lp" is the lateral distance between the pivot position 104 and the contact portion 103, and "lh" is the lateral distance between the position 105 where the fluid force is applied and the contact portion 103.
According to equation (1), it is necessary that the distance lh becomes long and a distance between the position 105 and the pivot position 104 is short, in order to keep the contact force fc at a low level. However, in the prior art taper-flat type slider, it is difficult to set the distance lh to be long, because the position 105 is located along the rotating direction of the disk 101 from the center of the total length of the slider 100.
The variation of the contact force fc according to the positioning error between the slider surface 102 and the contact portion 103 will be described.
As shown in FIG. 14, the slider 100 has three degrees of freedom. They are pitching(108), rolling(107), and translational(106) degrees of freedom. Stiffness of the fluid film between the slider surface 102 and the surface of the disk 101 keeps the condition of the slider 100 stable with regard to the three degrees of freedom. For example, the pitching stiffness will be described with reference to FIGS. 15(a)-l5(c). FIG. 15(b) shows the standard condition of the slider. If the angle .alpha.' formed between the slider surface 102 and the surface of the disk 101 (pitch angle) becomes smaller than the pitch angle .alpha. in the standard condition, as shown in FIG. 15(a), moment 109 occurs to restore the pitch angle. If the pitch angle .alpha." becomes larger than the pitch angle .alpha. in the standard condition, as shown in FIG. 15(c), moment 110 also occurs to restore the pitch angle. According to the prior art taper-flat type slider, the slider surface 102 is formed long enough to secure the pitching stiffness in the rotating direction of the disk.
When a positioning error between the slider surface 102 and the contact portion 103 is made, the contact force fc varies. This variation of the contact force fc will be described with reference to FIGS. 16(a)-16(c).
FIG. 16(b) shows the standard condition. FIG. 16(a) shows the condition that the contact portion 103 extends further than the contact portion of the standard condition. In this case, as the pitch angle .alpha.' in FIG. 16(a) becomes smaller than the pitch angle .alpha. in the standard condition, the moment 109 occurs to restore the pitch angle. Therefore, the contact force increases by dfc to balance the moment 109.
FIG. 16(c) shows the condition that the contact portion 103 is recessed relative to the contact portion of the standard condition. In this case, as the pitch angle .alpha." becomes larger than the pitch angle .alpha. in the standard condition, the moment 110 occurs to restore the pitch angle. therefore, the contact force decreases. Finally, the contact force fc becomes zero, and the slider 100 floats above the disk 101.
The influence of inertia which occurs due to the undulation of the disk, the vibration of the disk, or shock applied to the device from outside will be described with reference to FIG. 17. The inertia fg is applied at the center of gravity of the head (G) depending on the mass of the slider 100 and equivalent mass of the suspension (not shown). The position of G is located on the line connecting the center of gravity of the slider 100 (Gh) with the pivot position (Gp) where the equivalent mass of the suspension is applied. The inertia fg is divided between the variation of the fluid force dfh and the variation of the contact force dfc. The variation of the contact force dfc is shown in the following equation (2). ##EQU2##
"lg" is the lateral distance between the position of G and the contact portion 103.
According to equation (2), it is necessary for the distance lh between the position 105 where the fluid force is applied and the contact portion 103 to be long and for the position 105 to be located near the position of G in order to reduce the variation of the contact force dfc. But, in the prior art taper-flat type slider, it is difficult to set the distance lh to be long, because the position 105 and the pivot position (Gp) are located along the rotating direction of the disk 101 from the center of the total length of the slider 100.
A phenomenon of stiction between the head and the disk will be described. In a prior art magnetic disk drive having a flying type slider, the slider lands on the disk and the slider surface is kept in contact with the surface of the disk, when the disk stops rotating. It is called a constant.cndot.start.cndot.stop method (CSS method) as usual. According to the CSS method, stiction occurs by the influence of water or lubricant existing between the slider and the disk. Stiction prevents the disk from starting to rotate. In the prior art, the surface of the disk is made uneven to prevent stiction. However, it is necessary for the surface of the disk to be flat in the case of contact reading/writing. so that the the contact condition is stable. Therefore, stiction is a significant problem in the practice of contact reading/writing.